Silicon-germanium-based compositions comprising silicon, germanium, and carbon (i.e. Si-Ge-C), methods for growing Si-Ge-C epitaxial layers(s) (42) on a substrate (32), etchants especially suitable for Si-Ge-C etch-stops (42), and novel method of use for Si-Ge-C compositions are provided. In particular, the invention relates to Si-Ge-C compositions, especially for use as etch-stops and related processes and etchants useful for microelectronic and nanotechnology fabrication.

Silicon-germanium-carbon compositions and processes thereof

Molecular beam epitaxial growth of Si1−yCy alloys pseudomorphically strained on the (2×1) reconstructed Si(001) has been investigated as a function of growth conditions. An important question concerns the relation between substitutional and interstitial carbon incorporation, which has a large impact on electrical and optical properties of these layers. We show that the interstitial‐to‐substitutional carbon ratio is strongly influenced by the growth conditions, such as growth temperature and Si growth rate. Both reduction in growth temperature and increase of the overall growth rate lead to an increase in the substitutional‐to‐interstitial carbon ratio. However, these changes in growth conditions can also cause some deterioration in crystal quality. The carbon incorporation behavior is well described by first order kinetics.

Substitutional versus interstitial carbon incorporation during pseudomorphic growth of Si1−yCy on Si(001)

Photoluminescence of strained Si1−x−yGexCy alloys grown by rapid thermal chemical vapor deposition on Si(100) is investigated Two dominant features are reported: At low pump intensities, the photoluminescence is dominated by a deep level broad luminescence peak around 800 meV whereas at high pump intensities, a well‐resolved band‐edge luminescence (no phonon and transverse optic replica) is observed At 77 K, we attribute this band‐edge feature to an electron‐hole plasma luminescence of the ternary alloy The dependences of the deep level and band‐edge peaks versus the excitation power density are, respectively square‐root‐like or superlinear A blue shift of the energy gap of Si1−x−yGexCy alloys with respect to Si1−xGex alloy is observed The blue shift increase with carbon content corresponds to what is expected for the bulk alloy An eventual influence of the strain relaxation cannot be excluded

Band‐edge and deep level photoluminescence of pseudomorphic Si1−x−yGexCy alloys

Advances made in the growth and properties of CSi and CSiGe pseudomorphic strained layers are reviewed. The solubility of C in Si is small (3.5*1017 atoms/cm3 near the melting point). However, high-quality strained layers of the alloys with considerably larger C concentrations have been grown using MBE, CVD and solid-phase epitaxy methods. A careful control of the growth rate and temperature is necessary to avoid formation of silicon carbide. In high-quality layers, most of the C atoms occupy lattice positions of the Si or SiGe host crystals and a substitutional alloy is formed although the equilibrium volume of C atoms is only 30% of that of Si. The formation and stability of alloys of atoms with large differences in size is a topic of fundamental interest. Experimental and theoretical investigations have focused on the microscopic structure of substitutional Si1-x-yGexCy alloys. C compensates the compressive strain produced by Ge in the pseudomorphic layers grown on a Si substrate. From Raman studies of the microscopic strain in substitutional Si1-x-yGexCy alloys it has been concluded that Si-Si bonds experience a considerable local deformation even in strain-compensated alloys. The pair interaction of substitutional C atoms in an Si lattice and the possibility of forming ordered alloys have been studied theoretically. It has been found that the interaction of pairs of substitutional C atoms is attractive for special atomic configurations. Information available on electronic properties is rather meagre. Recent theoretical work shows that the bandgap of the alloy should decrease with C concentration. Experiments to confirm this have not yet been performed. Using strain-compensated alloys it is possible to grow symmetrically strained superlattices without the need of growing buffer layers. Si1-x-yGexCy strained layers are likely to be very useful for passive applications such as buffer layers. Considerably more work is required to determine their utility for active device applications.

http://iopscience.iop.org/article/10.1088/0268-1242/10/10/001/pdf

Growth and properties of strained Si1-x-yGexCy layers

We report the first Si/Si/sub 1-x-y/Ge/sub x/C/sub y//Si n-p-n heterojunction bipolar transistors and the first electrical bandgap measurements of strained Si/sub 1-x-y/Ge/sub x/C/sub y/ on Si (100) substrates. The carbon compositions were measured by the shift between the Si/sub 1-x-y/Ge/sub x/C/sub y/ and Si/sub 1-x/Ge/sub x/ X-ray diffraction peaks. The temperature dependence of the HBT collector current demonstrates that carbon causes a shift in bandgap of +26 meV/%C for germanium fractions of x=0.2 and x=0.25. These results show that carbon reduces the strain in Si/sub 1-x/Ge/sub x/ at a faster rate than it increases the bandgap (compared to reducing x in Si/sub 1-x/Ge/sub x/), so that a Si/sub 1-x-y/Ge/sub x/C/sub y/ film will have less strain than a Si/sub 1-x/Ge/sub x/ film with the same bandgap.

P. Boucaud

Papers

Growth and characterization of strain compensated Si1−x−y epitaxial layers